El Nino Episodes Research Articles

Spatial variation of different rain systems during El Niño and La Niña periods over India and adjoining ocean

The spatial patterns of rainfall and rain systems during El Nino and La Nina episodes are distinctly different due to the longitudinal variations in the Walker circulation ascent/decent branches over India and adjoining Oceans. In order to examine these differences, 16 years (1998–2013) of Tropical Rainfall Measuring Mission (TRMM) Precipitation Radar (PR) data have been utilized. TRMM-PR delineated precipitating systems (convective, stratiform and shallow) show distinctly different spatial structures over India and adjoining Oceans during El Nino and La Nina episodes. During the El Nino episode, the occurrence of deep systems is high over north of 20°N latitude, and shallow systems are plentiful over south of 20°N latitude. On the other hand, during the La Nina episodes, the occurrence of shallow systems is in excess over Pakistan, central India, northwest Arabian Sea, southwest Indian Ocean and northern Bay of Bengal while the deep systems are abundant over west coast of India, Ganges basin, eastern Indian Ocean and Arabian Sea. The excess convective rain pixels observed during El Nino years are from deep and deep and wide convective core systems due to increase in the CAPE, nevertheless the broad stratiform rain systems are prevalent during La Nina years due to the high convergence of moisture flux and mid-tropospheric upward motion. Though the convective occurrence is more, their intensity is weaker during El Nino years than during La Nina years, indicating the intense nature of convective storms during La Nina episodes.

Global mean sea level variations and the land water cycle at the inter-annual scale during the 2014–2016 El Niño episode

Since 1993, the global mean sea level (GMSL) has been rising at a rate of about 3 mm/a detected by multi-satellite radar altimetry. The spaceborne gravimetry satellite, Gravity Recovery and Climate Experiment (GRACE), has been monitoring Earth’s surface water mass variations since 2002. La Nina and El Nino events induces inter-annual variations of the GMSL manifest in ocean mass and steric sea level changes, linked with corresponding changes in land water cycle. Here we study the GMSL inter-annual variations and global land water mass changes integrating satellite altimetry, GRACE and Argo data, 2010–2016, during which strong La Nina and El Nino events occurred. First, we quantify the evolutions of GMSL during the study time period. The results show that during the 2010–2011 La Nina episode, the GMSL dropped rapidly to 7.6 mm, with the ocean mass and the steric sea level decreased to 5.1 mm and to 1.8 mm, respectively. GMSL then increased to 19.2 mm, with ocean mass increased to 12.3 mm during 2011–2013. From 2013 to 2014, the steric GMSL increased by 2.1 mm, and the ocean mass variations dropped by 2.3 mm, thus the total GMSL remains nearly unchanged. During the strong 2014–2016 El Nino, ocean mass variations increased by 13.1 mm and contributed over 90% of GMSL change, which rises up by 15.1 mm. Next, we analyze land water mass changes in four regions, namely Australia and Southeast Asia, South America, North America, Antartica and Greenland, and investigate their linkage to the GMSL inter-annual variations. Here, we used the Forward Modelling (FM) method for GRACE data post-processing to reduce signal leakage problem to estimate land water storage mass changes. The results show that during the 2014–2016 El Nino episode, the global ocean mass increasing is mainly due to the total land water storage decreasing in Australia and Southeast Asia, South America, and Antartica and Greenland. The inter-annual variations of global ocean mass variation during 2003–2016 is closely linked with the land water storage changes from Australia and Southeast Asia and the South America regions, which are strongly affected by La Nina and El Nino events. During 2003–2016, the ice ablations from the Antartica and Greenland ice sheets directly contributed to GMSL rising, as opposed to the land water mass increase in the North America region, which has a negative effect on GMSL trend. Finally, we estimated the GMSL, ocean mass and steric sea level trends at 3.4±0.4, 2.1±0.3, and 1.1±0.2 mm/a, respectively during 2003–2016, and 6.5±1.2, 4.1±1.0, and 1.9±0.4 mm/a, respectively during 2010–2016. We concluded that the ocean mass variation contributed to the GMSL trend two times larger than that of the steric sea level contribution during these two time periods. However the ocean mass variation is roughly equivalent to the steric sea level variation during 2003–2010.

Paleomagnetic and paleoclimatic investigation at Laguna Melincue (Pampean Plains, Argentina): preliminary results

Laguna Melincue is a shallow lake located in Santa Fe Province, Argentina (33°41′27.8″S, 61°31′36.5″W). The catchment area is around 1495 km2 and it is located in the Pampean Plains. It was reduced to 678 km2 by the construction of the San Urbano channel in 1941 and reconditioned in 1977, which was built to avoid floods. The floods are related to some El Nino episodes, with high precipitation events. The lake has been previously studied from different approaches, mainly to understand hydrological and climatic variations, but more multidisciplinary studies are needed to understand its complex hydrological situation. Here we present the first paleomagnetic and rock magnetic studies made on a short sediment core collected from the lake in order to contribute to identifying paleoclimatic proxies and to present the first paleomagnetic results for the site. Rock magnetic analyses suggest that the well-preserved magnetic mineralogy is dominated by pseudo single-domain (titano)magnetite and/or maghemite. The results also indicate that a stable characteristic remanent magnetisation can be isolated and thus the directions of the geomagnetic field may be obtained, providing evidence for the use of this lake for paleomagnetic and paleoenvironmental studies. Changes in magnetic grain size and concentration of magnetic minerals suggest environmental variations and changes in the lake level, which are consistent with historical reports. The paleomagnetic results agree well with Cals3k.3 model for inclination and declination of the geomagnetic field except for the dry period probably due to the fact that the core was extracted near the shore.

The Effects of El Nino on Agricultural GDP of Ethiopia

End hunger, achieve food security and improve nutrition is at the heart of the sustainable development goals. At the same time, climate change is already impacting agriculture and making the challenge even more difficult. In many parts of the world, much of the year-to-year variation in climate is traced to the El Nino episode. This paper uses El Nino Southern Oscillation (ENSO) index to examine the effect of El Nino shock on agricultural GDP of Ethiopia. The paper employed Vector Autoregressive (VAR) model in analysing 26 years time series data. Before regressing the data, activities such as lag selection, unit root test, Johansen Cointegration test, and diagnostics test were done. The result of the study shows that an incidence of El Nino phenomena truncate agricultural GDP of Ethiopia by 13.59 percent. The result is statistically significant at less than 5 percent significant level. And also 92.66 percent of the total variation in the model is explained by the explanatory variables. Thus the nation should work hard in adoption of water harvesting technology, irrigation, drought resistance and perennial crops to mitigate the consequence of El Nino shock.

Impact of climate change and El Niño episodes on droughts in sub-Saharan Africa

Various drought prone regions of sub-Saharan Africa (SSAF) have been affected by severe droughts in recent decades and centuries, which had caused catastrophic humanitarian crisis. In this study, the Palmer Drought Severity Index was used to analyse changes in drought characteristics of SSAF during 1971–2000 and the Representative Concentration Pathways (RCP4.5 and RCP8.5) climate projections of selected GCMs (Global Climate Models) for the 2041–2070 (2050s) and 2071–2100 (2080s) periods. The results show that most areas in South Africa (SA) and West Africa (WA) will shift to a drier climate in the 2050 and 2080s. However, some areas in Greater Horn of Africa (GHA) are expected to be relatively wetter in the 2050 and 2080s whereas very little change is projected in the average drought severity of Central Africa (CA). The frequency of short (6–12 months) and long (above 12 months) drought events also increased on average by 5 %. However, a 1–6 % decrease in the average duration of long drought periods was projected during the 2050 and 2080s likely due to the increase in the intensity and frequency of extreme precipitation events in SSAF. An increase in the frequency of El Nino episodes under a warmer twentyfirst century climate is also expected to increase the drought prone regions of WA, SA and particularly GHA while CA still remains virtually unaffected. Overall, the results suggest that SSAF will experience a drier climate in the 2050 and 2080s with an increase in drought prone areas in the four corners of the sub-continent.

The strong El Niño of 2015/16 and its dominant impacts on global and China's climate

The oceanic and atmospheric conditions and the related climate impacts of the 2015/16 ENSO cycle were analyzed, based on the latest global climate observational data, especially that of China. The results show that this strong El Nino event fully established in spring 2015 and has been rapidly developing into one of the three strongest El Nino episodes in recorded history. Meanwhile, it is also expected to be the longest event recorded, attributable to the stable maintenance of the abnormally warm conditions in the equatorial Pacific Ocean since spring 2014. Owing to the impacts of this strong event, along with climate warming background, the global surface temperature and the surface air temperature over Chinese mainland reached record highs in 2015. Disastrous weather in various places worldwide have occurred in association with this severe El Nino episode, and summer precipitation has reduced significantly in North China, especially over the bend of the Yellow River, central Inner Mongolia, and the coastal areas surrounding Bohai Bay. Serious drought has occurred in some of the above areas. The El Nino episode reached its peak strength during November-December 2015, when a lower-troposphere anomalous anticyclonic circulation prevailed over the Philippines, bringing about abnormal southerlies and substantially increased precipitation in southeastern China. At the same time, a negative phase of the Eurasia-Pacific teleconnection pattern dominated over the mid-high latitudes, which suppressed northerly winds in North China. These two factors together resulted in high concentrations of fine particulate matter (PM2.5) and frequent haze weather in this region. Currently, this strong El Nino is weakening very rapidly, but its impact on climate will continue in the coming months in some regions, especially in China.

Impact of El Niño and Climate Change on Rainwater Harvesting in a Caribbean State

The water situation of the Pusey district in St Catherine parish of Jamaica is acute because of the district’s hilly terrains which made connections to centralised public water supply difficult. Residents depend on rainwater harvesting (RWH) systems to meet potable needs, like many other catchments across Jamaica. Rainwater collecting practices and water use habits of the residents were surveyed and the present and future RWH capacity was evaluated using the available 18 years (1996 to 2013) rainfall data and downscaled PRECIS model A2 and B2 climate change scenarios. In addition, the effect of El Nino episodes on rainfall patterns was evaluated. The coefficients of variations for annual rainfall were found to be higher for the El Nino years than in normal years. In two of the El Nino years (1997 and 2009), rainwater harvesting capacity is negatively impacted as rainfall annual total is (42 % and 34 %) lesser than the average annual rainfall. The ability of RWH to meet potable needs in 2030s and 2050s will be reduced based on predicted shorter intense showers and frequent dry spells. A storage tank of 2.5 to 4.0 m3 per household (4 persons) is proposed to meet water demand during the maximum consecutive dry days, and January and February water shortage periods. Design of efficient RWH systems and provision of government subsidy on storage tanks will enable the residents to capture more rainwater to meet their daily domestic needs.

The impact of eastern equatorial Pacific convection on the diversity of boreal winter El Niño teleconnection patterns

It is widely recognized that no two El Nino episodes are the same; hence the predictable variations of the climate impacts associated with El Nino remain an open problem. Through an analysis of observational data and of large ensembles from six climate models forced by the observed time-varying sea surface temperatures (SSTs), this study raises the argument that the most fundamental predictable variations of boreal wintertime El Nino teleconnection patterns relate to the distinction between convective (EPC) and non-convective eastern Pacific (EPN) events. This distinction is a consequence of the nonlinear relationship between deep convection and eastern Pacific SSTs, and the transition to a convective eastern Pacific has a predictable relationship with local and tropical mean SSTs. Notable differences (EPC minus EPN) between the teleconnection patterns include positive precipitation differences over southern North America and northern Europe, positive temperature differences over northeast North America, and negative temperature differences over the Arctic. These differences are stronger and more statistically significant than the more common partitioning between eastern Pacific and central Pacific El Nino. Most of the seasonal mean composite anomalies associated with EPN El Nino are not statistically significant owing to the weak SST forcing and small sample sizes; however, the EPN teleconnection is more robust on subseasonal timescales following periods when the EPN pattern of tropical convection is active. These findings suggest that the differences between EPC and EPN climate impacts are physically robust and potentially useful for intraseasonal forecasts for lead times of up to a few weeks.

Sea surface temperature anomalies in the South China Sea during mature phase of ENSO

Based on the 18-year (1993–2010) National Centers for Environmental Prediction optimum interpolation sea surface temperature (SST) and simple ocean data assimilation datasets, this study investigated the patterns of the SST anomalies (SSTAs) that occurred in the South China Sea (SCS) during the mature phase of the El Nino/Southern Oscillation. The most dominant characteristic was that of the outof-phase variation between southwestern and northeastern parts of the SCS, which was influenced primarily by the net surface heat flux and by horizontal thermal advection. The negative SSTA in the northeastern SCS was caused mainly by the loss of heat to the atmosphere and because of the cold-water advection from the western Pacific through the Luzon Strait during El Nino episodes. Conversely, it was found that the anomalous large-scale atmospheric circulation and weakened western boundary current during El Nino episodes led to the development of the positive SSTA in the southwestern SCS.

Heavy rainfall patterns in Vietnam and their relation with ENSO cycles

Heavy rainfall months of more than 450 mm occur in all 56 meteorological stations in eight climatic zones of Vietnam during the rainy season from April to September in the north (>20°N), from August to December in the centre and from May to November in the south (<12°N). The severity of an El Nino Southern Oscillation (ENSO) episode, expressed as the integral of sea surface temperature anomaly (SSTA) in the central tropical Pacific over the duration, shows a 4.6-fold (2.3-fold) increase in number of heavy rainfall months during La Nina (El Nino) per unit change in severity during the 1960–2009 period, suggesting a twin peak occurrence with both ENSO extremes. A heavy rainfall index (HRI) links heavy rainfall months to the rainy season duration, and allows evaluation of the rainfall severity per station, climatic zone and ENSO cycle. For the deltas and central climatic zones, seasonal rainfall and number of heavy rainfall months are significantly higher at the p < 0.05 level during La Nina than during El Nino episodes. Interpolated seasonal rainfall shows distinct differences between regions, with location having a larger effect than ENSO cycles on monthly rainfall amounts. Twenty-year return monthly rainfall derived from generalized Pareto distributions for peak over thresholds range from 475 mm in the central highlands to 2185 mm in the central coast. The spatial and temporal patterns of heavy monthly rainfall help explain flooding and paddy inundation which occur at least twice as frequent during La Nina as compared to El Nino conditions, particularly in Central Vietnam. The relation of HRI with both 20-year return levels and ENSO cycles offers opportunities for fast screening of impacts in a wider region of Southeast Asia. Because ENSO cycles have an impact on flooding and paddy inundation, it provides prospects for early warning, differentiated for different zones and rainfall regimes.

Future Irrigation Demand of South Saskatchewan River Basin under the Combined Impacts of Climate Change and El Niño Southern Oscillation

We assessed the future irrigation demand of the South Saskatchewan River Basin (SSRB) of Alberta subjected to combined impact of climate change and El Nino Southern Oscillation (ENSO) using the Irrigation District Model (IDM) of Alberta Agriculture and Rural Development. Based on the agro-climatic data of SSRB of 1928–1995, the potential impact of climate change on SSRB’s irrigation water demand for three future periods, i.e., 2010–2039 (2020s), 2040–2069 (2050s), 2070–2099 (2080s) are simulated by IDM on the basis of Special Report on Emissions Scenarios (SRES) climate scenarios projected by four General Circulation Models (GCMs) of Intergovernmental Panel on Climate Change (IPCC). The combined impact on SSRB’s irrigation water demand is also simulated on the basis of SRES climate scenarios together with an active El Nino or La Nina in the 2050s. If only the potential impact of climate change is considered, IDM’s simulations for 2020s, 2050s, and 2080s show a general increasing trend in the irrigation demand in the 21st century for both the irrigation districts and the private irrigation blocks. On the average, water demands for the irrigation districts and private irrigation blocks are expected to increase by 7% and 11% in the 2020s, 12% and 17% in the 2050s, and 13% and 18% in the 2080s, respectively. While considering the combined impact for the 2050s, a further 7% decrease (1% increase) in the irrigation demand is projected under an active El Nino (La Nina) episode.

Has modulation of Indian summer monsoon rainfall by sea surface temperature of the equatorial Pacific Ocean, weakened in recent years?

In this paper, the east–west tropical ‘Walker circulation’ and its linear association with sea surface temperature (SST) of the Nino 3 region and Indian summer monsoon rainfall (ISMR) have been investigated. ‘Walker circulation’/‘reverse Walker circulation’ is primarily forced by SSTs of the equatorial Pacific Ocean. In this study, velocity potential field of 0.21 sigma level over the tropics was considered as proxy of the zonal tropical circulation (‘Walker circulation’/‘reverse Walker circulation’). Principal component analysis of the monsoon season tropical velocity potential data of 0.21 sigma level for the two periods 1951–1980 and 1981–2010, was done separately. We find that earlier, two different patterns of the velocity potential field, forced by probably two distinct modes of El Nino episodes, were associated with the ISMR. These two El Nino episodes, respectively, correspond to the strong El Nino events, where in warming was extended up to the date line (primarily zonal) and the moderate El Nino events in which, warming having north south extension, was limited to the eastern Pacific Ocean only. However, in recent years, only the first pattern of the velocity potential field, induced by the strong El Nino events (warming extending up to the date line), was correlated with the ISMR. Further, in the later period (1981–2010), velocity potential field at 0.21 sigma level over the tropical Pacific and Indian Oceans, which appeared to be primarily driven by SST anomalies of the equatorial Pacific Ocean in the first period, was found to be significantly correlated with the extra tropical circulation anomalies also. Therefore, modulation of the ISMR through velocity potential field over the tropical Indian and Pacific Oceans, in the later period, may have additional significant impact of the extra-tropical circulation anomalies. This might have led weak correlation between the ISMR and SSTs of the Nino 3 region, which is actually being observed in recent years.

Analysis of Climate Variability (ENSO) and Vegetation Dynamics in Gojjam, Ethiopia

This study analyses the regional climate variability, especially La Nina or El Nino Southern Oscillation events and their impact on rainfall variability and vegetation coverage. The temporal and spatial distributions of temperature, precipitation, and vegetation coverage have been investigated for the two agricultural productive seasons from (2000–2008), using data from 11 meteorological station and MODIS satellite data in Gojjam, Ethiopia. The normalized difference vegetation index (NDVI) is widely accepted as a good indicator for providing vegetation properties and associated changes for large spatial scale. The analyses indicated that climate variability is quite common particularly in the small rainy season, Belg and continues to affect the vegetation condition in the region. The statistical correlation analysis indicated that there is a strong positive correlation between NDVI and the seasonal rainfall in most years, whereas, the temperature increase decreases the vegetation coverage in both seasons. The effect of ENSO, climate variability has been high to the regional rainfall variability in mostly of the months or years. In the fully strong El Nino or La Nina episode years like 2000 and 2002 the SST and rainfall showed positive correlation with r2 values 0.75 and 0.63, respectively. The NDVI anomaly pattern is almost similar to that of the main documented precipitation and temperature anomaly pattern associated with ENSO. The spatial and temporal analyses of basic climate elements and NDVI values for the growing season showed that NDVI and rainfall are highly variable during the 9 years period. The ENSO analyses showed an increase in seasonal vegetation coverage during El Nino episodes contrasting to La Nina episodes. However, there has been a rainfall delay during El Nino episodes in the first one or two months of Kiremt season.

Fair Weather or Foul? The Macroeconomic Effects of El Niño

This paper employs a dynamic multi-country framework to analyze the international macroeconomic transmission of El Nino weather shocks. This framework comprises 21 country/region-specific models, estimated over the period 1979Q2 to 2013Q1, and accounts for not only direct exposures of countries to El Nino shocks but also indirect effects through third-markets. The results of our Global VAR model of the world economy indicate that the economic consequences of El Nino shocks differ across countries. While Australia, Chile, Indonesia, India, Japan, New Zealand and South Africa face a short-lived fall in economic activity in response to an El Nino shock, for other countries, the El Nino shock has a growth-enhancing effect; some (for instance the U.S.) due to direct effects while others (for instance the European region) through positive spillovers from major trading partners. Furthermore, most countries in our sample experience short-run in inflationary pressures as both energy and non-fuel commodity prices increase. Given these findings, macroeconomic policy formulation should take into consideration the likelihood and effects of El Nino episodes.

O centróide da piscina de água quente do pacífico como um indicador dos fenômenos El Niño e La Niña

Os fenômenos oceanográficos El Niño e La Niña foram analisados através do monitoramento da série temporal da componente zonal do centroide da piscina de água quente do Pacífico (PAQ) que descreve movimentos leste-oeste ao longo da faixa intertropical deste oceano. Utilizou-se uma série de dados de temperatura da superfície do Oceano Pacífico para classificar a PAQ e estimar o seu centroide entre 1981 e 2003. Todos os episódios de El Niño (1982-83; 1986-87; 1990-95; e 1997-98) e La Niña (1984-85; 1988-89; 1998-2000) existentes no período analisado puderam ser observados na série temporal de dados da componente zonal da PAQ (CZPAQ). Os episódios mais intensos de El Niño foram classificados pela ordenação decrescente dos maiores deslocamentos para leste (ranking). A série de dados da CZPAQ se apresentou em fase com o índice de Oscilação Sul e com a anomalia da temperatura superficial do oceano (TSO). As flutuações associadas ao movimento zonal do centroide da PAQ foram observadas no espectro de energia onde ficaram ressaltadas as flutuações interanuais associadas aos fenômenos El Niño e La Niña. Foram observados deslocamentos mais curtos para oeste durante os anos de La Niña, quando comparados aos deslocamentos para leste durante os eventos de El Niño. A migração zonal da PAQ, representada aqui pelo centroide, apresentou-se, portanto, como um indicador dos fenômenos El Niño e La Niña. A principal vantagem dessa técnica é a dependência de um único parâmetro arbitrário, que é o limiar da TSO para delinear a PAQ.

Possible North Atlantic origin for changes in ENSO properties during the 1970s

The most intense El Nino episodes in more than a century occurred after the 1970s climate shift. Previous studies show that the characteristics of the El Nino-Southern Oscillation (ENSO) phenomenon changed synchronously with the shift, but the associated causes are not fully understood. An analysis of the observed tropical Pacific sea surface temperature (SST) anomalies shows that their increase in the eastern part of the basin after the 1970s is not related to the canonical ENSO pattern, but to the tropical Pacific meridional mode (TPMM). We present observational evidence which supports the hypothesis that the change in the TPMM was triggered by the great salinity anomaly (GSA), which manifested in the North Atlantic during the late 1960s. The GSA induced a weak Labrador convection and a SST dipole south of Greenland. The associated atmospheric structure includes a North Pacific Oscillation sea level pressure dipole in the Pacific sector. This excites the TPMM which contributes to the intense El Nino events and to the enhanced ENSO’s asymmetry, observed after the shift. Our results imply that, if the GSA has not an anthropic origin, as was suggested, then the tropical Pacific climate shift has a natural origin. This is supported by the end of the North Atlantic regime in the 1990s and by the rebound of the tropical Pacific after 1998.

A general regional frequency analysis framework for quantifying local-scale climate effects: A case study of ENSO effects on Southeast Queensland rainfall

Summary There is increasing evidence that the distribution of hydrometeorological variables such as average or extreme rainfall/runoff is modulated by modes of climate variability in many regions of the world. This paper presents a general spatio-temporal regional frequency analysis framework that allows quantifying the effect of climate variability on the distribution of at-site hydrometeorological variables. Climate effects are described through the parameters of a pre-specified distribution, by using regression models linking parameter values with time-varying covariates, such as climate indices. For the regional model copulas are used to incorporate spatial dependency. A Bayesian framework is used for inference and prediction, which enables quantification of parameter and predictive uncertainties. A regional approach enables better identification of climate effects which can be subject to high uncertainty using only at-site (local) analysis. Lastly, model comparison tools enable considering competing statistical hypotheses on the nature of climate effects and selecting the most relevant one. This modelling framework is applied to two case studies assessing the effect of El Nino Southern Oscillation (ENSO) on summer rainfall in Southeast Queensland. The first case study focuses on summer rainfall totals while the second analysis focuses on extremes using summer daily rainfall maxima. The Southern Oscillation Index (SOI), a measure of ENSO, is considered as a time-varying covariate. In order to account for different effects during La Nina and El Nino episodes, an asymmetric piecewise-linear regression is used to analyse the rainfall data using both local and regional models. During La Nina episodes, SOI has a significant effect on both summer rainfall totals and maxima. Conversely, during El Nino episodes, the SOI has little effect on rainfall. It is found that, during a strong La Nina, the most likely 1 in 100 year summer maximum daily rainfall for different sites estimated with the local asymmetric model can be 5–33% higher than the estimates from a local symmetric linear model and 20–50% higher than the estimates from a stationary model, albeit with significant uncertainty. Results from regional and local models are also compared: the former shows a great advantage in terms of uncertainty reduction and allows a better quantification of the ENSO effect on summer rainfall totals and maxima.

A boost in big El Niño

Computer models and theory do not offer a consensus on how El Nino will change under global warming. Despite this disagreement, a study indicates a robust increase in the frequency of extreme El Nino episodes.

A new index for variations in the position of the South Pacific convergence zone 1910/11–2011/2012

Quality controlled and recently homogenised mean sea level pressure records for the South Pacific are used to specify the location and variability of the South Pacific convergence zone (SPCZ) during the austral warm season (November–April). The SPCZ is the world’s largest rainfall band during the austral summer, when it dominates the climate of the South Pacific. A new index called the South Pacific convergence zone index (SPCZI) is derived, and is shown to be coherent with changes in low level wind convergence associated with the SPCZ. This index replaces the earlier SPCZ position index because it uses higher quality mean sea level pressure data than the superseded index and extends the time series further forward in time. The SPCZI allows interannual to decadal variability in the climate of the South Pacific to be tracked for more than a century from 1910/1911 to 2011/2012. During El Nino episodes the SPCZ is displaced by about 1°–3° east, and La Nina events 1°–3° west of the mean position on average. The index indicates a striking movement eastward for the period 1977/78–1998/99, compared with 1944/45–1976/77 in association with the Interdecadal Pacific oscillation (IPO). The eastward movement of the SPCZ in the late twentieth century is related to significant precipitation trends in the South Pacific region. Since 1998/99 the SPCZ has regressed westward with the negative phase change of the IPO. The long-term trend in the SPCZI is very small relative to the interannual to decadal variability and is not statistically significant, suggesting that there has been little overall change in the mean position of the SPCZ over the past century.

Modeling the Effect of Environmental Factors on the Ricker Stock-Recruitment Relationship for North Pacific Albacore Using Generalized Additive Models

This study investigates how the inclusion of El Nino episodes affects the modeling of recruitment in North Pacific albacore. The relationship between spawning stock size and recruitment for the 1976 - 2004 period, including environmental variables (Southern Oscillation Index and sea surface temperature anomalies), was conducted by general linear and generalized additive models (GAM). The results indicate that the Southern Oscillation Index and the interaction between spawning stock size and sea surface temperature anomalies have significant effects on the recruitment of North Pacific albacore. GAM fit the original data better than general linear models, according to the Akaike information criterion. The recruitment declined when El Nino episodes occurred, but increased when La Nino episodes occurred. The recruitment also increased when the spawning stock size density was above 11.21 million tons with a -0.3°C sea surface temperature anomaly. El Nino was observed to have both long-period (above 10 - 15 years) and short-period (1 - 2 years) effects on North Pacific recruitment.